I just got a new lemonblast BP. I came here looking for info on this very issue. My little guy is only 5 moths old and I just fed him for the first time. He did the very same thing as the OP's BP. I have not seen him shake any other time except when he took his food. He also made his neck into an "s" shape to make the prey go down if that makes sense? Would love to know more about this. Anyone have anymore info?